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An annual summary of nuclear warhead convoy movements in 2012, published by the Nukewatch network, suggests that the UK is making progress with the programme to reduce warhead numbers which was announced in the 2010 Strategic Defence and Security Review.

The record of convoy movements (available to download at the end of this article) suggests that British nuclear warheads continue to be transported from the Coulport nuclear arms depot in Scotland to the Atomic Weapons Establishment (AWE) for disassembly and removal from service - a trend first observed last year.

Nukewatch, which monitors the transport of nuclear weapons across the UK, considers that during 2012 at least four loaded convoys travelled between the Royal Naval Arms Depot Coulport, where the UK's stockpile of nuclear weapons is held, and the Atomic Weapons Establishment (AWE) at Burghfield in Berkshire.

As observed last year, there was a discrepancy in observations between the numbers of loaded convoys transporting warheads from Coulport to the Atomic Weapons Establishment and the number of loaded return journeys to Coulport. Nukewatch estimates that between three and six warheads - more likely at the lower end of this range - were retained at AWE. This would be consistent with a programme for bringing the UK's total warhead stockpile down from around 225 warheads to around 180 warheads by the mid 2020s, as the government committed to do in the 2010 Strategic Defence and Security Review (SDSR), although Nukewatch stresses that further monitoring over future years will be needed to confirm whether a gradual annual reduction in warhead numbers is indeed taking place.

The Ministry of Defence has confirmed that the UK is currently taking steps to remove warheads from service, corroborating the Nukewatch observations. In a letter to journalist Rob Edwards, an MoD official wrote:

“Since 2002, the Atomic Weapons Establishment (AWE) has been running a Stockpile Reduction Programme to disassemble Trident warheads to reduce stockpile numbers as declared in the Strategic Defence Review 1998, the 2006 White Paper on the Future of the United Kingdom’s Nuclear Deterrent and the SDSR. The warheads that have been identified as no longer required for service but are yet to be disassembled are stored at the Royal Naval Armaments Depot Coulport or as work in progress at AWE Burghfield. All warhead disassembly work is undertaken at AWE Burghfield.

“The main components from warheads disassembled as part of the stockpile reduction programme have been processed in various ways according to their composition and in such a way that prevents the warhead from being reassembled. A number of warheads identified in the programme for reduction have been modified to render them unusable whilst others identified as no longer being required for service are currently stored and have not yet been disabled or modified. This is in line with the overall target date to achieve the declared reduction by the mid 2020s”.

Nukewatch reported that convoy movements during the year took place at a higher level of activity than over the past three years, possibly because the Trident nuclear weapons submarine HMS Vengeance temporarily left service for refit at Devonport dockyard in March 2012, allowing warheads removed from the submarine to be returned to AWE for servicing.

Warheads are transported between Coulport and AWE on a regular cycle for maintenance and surveillance purposes, and Nukewatch concludes that the level of convoy activity continues to take place at the baseline level necessary to allow this, with an additional slow rate of return of warheads to AWE for decommissioning.

The Nukewatch report was compiled on the basis of spottings of nuclear convoys recorded by members of the network during 2012. Annual reports on convoy movements from Nukewatch are one of the few independent benchmarks which can be used to validate government statements on the size and status of the UK nuclear arsenal.

A copy of the Nukewatch annual summary of warhead convoy movements can be downloaded here: